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20 October 2021, Volume 27 Issue 5
Restoration and Characteristics Analysis of Paleochannels in Gentle Slopes of A Rift Basin: Dongying Formation of Baxian Sag, Bohai Bay Basin
2021, 27(5):  501-514.  DOI: 10.16108/j.issn1006-7493.2020085
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Quantitative analysis of fluvial sand body is important for efficient oilfield exploration and development. In this paper, quantitative core analysis, well logging facies analysis, quantitative seismic sedimentology, and 3D seismic profile identification are used to quantitatively calculate the thickness of paleochannel sand body, width of channel (belt), depth of channel and other river parameters of Dongying formation in Wen’an slope of Baxian sag. The analyses reveal that there are three provenance entrances in Dongying formation of Wen’an slope, Suqiao in the north, Wenan in the middle, and Changfengzhen in the south. The rivers flowed on the Wen’an slope in NEE-SWW directions. The width (W) of the channel belt is 1.04-2.61 km, and the average width (wcb) is 1.71 km; the width (W) of the main channel is 15.2-179.6 m, and the average width (Wc) is 84.4 m; the depth (D) of the main channel is 1.34-5.21 m, and the average depth (Dc) is 3.29 m; the full depth (Dmax) of the main channel is 2.35-9.15 m, and the average full depth (Dmax) is 5.77 m; the thickness (H) of the main channel is 2.15-8.32 m, the average thickness (Hc) is 5.25 m, the length of river channel (L) is 18.5-28.2 km, the average length of river channel belt (Lcb) is 25.1 km, and the flow direction is 40°-65°. It is considered that Dongying formation of Wen’an slope are braided river deposits. The outer zone of the

slope is the main unloading area of sandstone, the river is dominatly vertically excavated and supplemented by lateral migration,
and the plan view of channel sandstone is “strip belt”. The inner zone of Wen’an slope is dominated by laterally migrating rivers, supplemented by erosion, and channel sandstone occurs as a sheet blanket. The channel sandstone of Dongying formation has the sedimentary conditions of “lower generation and upper reservoir”, and the development of lithologic and structural lithologic reservoirs has a promising prospect for oil and gas exploration.

Geological and Geophysical Characterization of the Sedimentary Features on Braided River Delta in the Upper Member 3 of the Shahejie Formation, Kenli Oilfield, Laizhouwan Sag
ZHANG Jianmin, QIN Yi, GUO Cheng, CUI Longtao, LI Zhuo, JIN Lei, WANG Xiaoxue
2021, 27(5):  515-525.  DOI: 10.16108/j.issn1006-7493.2020082
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The upper Member 3 of the Shahejie Formation (E2s3U) in the KenLi (KL) Oilfield is the primary target strata for medium-deep oil and gas exploration in Laizhouwan Sag, Bohai Bay Basin. Integrating the analyses of sedimentary background, three-dimensional seismic, core, and well-logging data, using the seismic sedimentological technique, we studied on sedimentary characteristics and depositional evolution of the braided river delta formed during the E2s3U interval in KenLi Oilfield. The results show that braided river deltas developed in the study area received sediments from three source areas, namely Laibei Low Uplift, Kendong Uplift, and Weibei Low Uplift. The well-sorted sand bodies in the delta plain were mainly fine-medium sandstone; whereas the sand bodies in the delta front were fine sandstone and siltstone. Sedimentary structures were developed well under tractive currents. Additionally, wavy bedding and bioturbation structures are common, suggesting turbulent water conditions in the delta front environment. The oblique progradation reflections were developed along the source direction, and multi-unit mounded-shape seismic reflections were observed across the source direction. Comprehensive analyses of paleo-geomorphology, sedimentary characteristics, and amplitude attribute slices of strata reveal that the Laibei Low Uplift is the dominant source area, which provided abundant sediments to the depositional area. Middle and eastern districts of the sedimentary area were central depositional regions, where a large area of braided river delta deposits (95~130 km2) with landward-stepping was developed. Western and eastern districts of the sedimentary area were fed by multi source areas. The delta front from the Kendong Uplift gradually shrank, and the delta front from the Weibei Uplift gradually prograded basinward. Study on the sedimentary characteristics and evolution of depositional processes of the braided river delta systems will serve as a reference for reservoir prediction and oil exploration and development.

Characteristics and Significance of Carbonate Cements in Member 3 of Shahejie Formation in the Northern Subsag of Laizhouwan Sag
WANG Tong, ZHU Xiaomin, LIU Yu, GUO Cheng
2021, 27(5):  526-535.  DOI: 10.16108/j.issn1006-7493.2020084
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Based on the analyses of petrology, mineralogy, and geochemistry, this paper has studied the distribution, forming environment, material sources, precipitation temperature, and their impacts on the reservoir physical properties for Member 3 of Shahejie Formation sandstones in the northern subsag of Laizhowan sag. Results show that two periods of the cements are developed in the member: the carbonate cements in the early period are siderite and cryptocrystalline calcite, and the carbonate cements in late period are calcite, dolomite, ferrocalcite and ferrodolomite. Calcite is the main type of carbonate cements. The carbonate cements are formed in the high salinity environment in the middle and late stage of diagenesis, resulted from decarboxylation of organic acid. Organic carbon is the main carbon source. Feldspar dissolution and clay mineral transformation  provide abundant calcium for the carbonate development. The study of homogenization temperature of fluid inclusions indicates that carbonated cements are formed at or after the hydrocarbon filling. The carbonate cements formed in the early diagenesis can enhance the consolidation and compaction resistance ability for the rock skeleton particles to a certain degree; meanwhile they can also become the main corroded objects for the late organic acids and possess positive and improving effects on the physical properties of the reservoirs. The cements formed after dissolution often occupy the intergranular partially dissolved pores, so they are destructive to the physical properties of the reservoirs.

Sequence Stratigraphy and Sedimentary Filling of the Third Member of the Dongying Formation in the LD16 Oilfield, Liaozhong Sag
HUANG Kai, QIN Yi, LIU Zongbin, ZHU Jianmin, LIU Xilin, SHEN Tingting
2021, 27(5):  536-546.  DOI: 10.16108/j.issn1006-7493.2020083
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The third Member of the Dongying Formation (Ed 3) in the LD16 oilfield in the Bohai Bay Basin is the main target for oil and gas exploration. Following the study of comparison of well and seismic and sequence stratigraphy, integrated analyses on paleogeomorphology, core facies, well-logging facies, seismic facies, and amplitude attribute slices were conducted based on 3-D seismic, well-logging, and core data to clarify the sedimentary facies, distribution and evolution. Using the classic theory Vail sequence stratigraphy, we recognized one third-order sequence stratigraphic unit within the Ed3, which can be divided into lowstand system tract (LST), transgressive system tract (TST) and highstand system tract (HST). During the LST and TST stages, the Liaoxi Uplift was subject to an intense erosion due to the exposure. Fan delta and gravity flow deposit systems were well developed along of sufficient sedimentary supply. The sand bodies of fan delta are mainly medium- and fine-grained sandstones with well-developed sedimentary structures of lag deposits, wavy bedding, and bioturbation. During the HST stage, the Liaoxi Uplift was submerged, and the capacity of the sedimentary supply was weakened. Therefore, braided river delta front and gravity flow deposit systems were developed in the study area. The subaqueous distributary channels of braided river delta consist of medium-fine-grained sandstone with wedge cross-bedding. The gravity flow deposits are mainly slump-induced sub-lacustrine fan deposits with deformed structures and sandy-debris flow deposits, which show sandstones with floating pebbles and mud clasts. The depositional evolution is closely related to the paleo-geomorphic evolution in the study area. In addition, fault systems control the distribution of sand bodies. The gravity flow sand bodies commonly developed in the front of the fault slope-break zone. The research on sedimentary facies, distribution and evolution is helpful for further hydrocarbon exploration in the study area.

Genetic Analysis and Identification Method for High Resistivity Water Layer in the Dongying Formation of Bohai C Oilfield
WANG Miao, LI Ruijuan, XIONG Lei, LI Zhiyuan, GUAN Yeqin
2021, 27(5):  547-553.  DOI: 10.16108/j.issn1006-7493.2020089
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The sedimentary characteristics and diagenesis of the Dongying Formation in the Bohai C oilfield are complex, and the physical properties change greatly. Evidence for oil and gas is common. Because are a large number of high-resistivity water layers as shown in logging data, it is difficult to identify the fluid types. The comprehensive analyses of well-logging results, core, rock and mineral data reveal that the high content of clay minerals, dominantly kaolinite, and high residual oil saturation are the two main factors for the high resistivity water layers. Based on the analysis of the genesis, we propose that the fluid replacement method and the intersection of deep resistivity and density curves can be used to quickly identify high-resistivity water layers. The application of the methods with measurement data shows that the difference between normalized deep resistivity and density is a sensitive parameter for identifying oil and water layer, according to the crossplot of ΔRd -Δρ vs. Rd, the oil layer mainly occurs
in regions where ΔRd -Δρ is greater than 2.3. This method could guide comprehensive evaluation of well logging in C oilfield and
even in the medium-deep reservoirs of Bohai area.
Prediction of Seismic Facies-controlled Inversion for Delta Reservoir in the Eocene Middle Es-3 of the Laizhou Bay
PENG Gang, CUI Xuepeng, MING Jun, HUANG Handong, TANG Hebing, WANG Jianxing, LI Jiu, ZHAO Haifeng, WANG Hongning
2021, 27(5):  554-560.  DOI: 10.16108/j.issn1006-7493.2020086
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The Kenli 10-1 oilfield is located in the northern slope of the Laibei low uplift. The Eocene Shabejie Formation of key reservoir evaluation is a complex fault-block reservoir, and its main oil-bearing interval is in the No.Ⅰand No.Ⅱoil layers of the Middle Es-3 (ie., the third Member of the Shahejie Formation), which are dominated by braided river delta deposits and highfrequency prograding delta deposits respectively. The delta is characterized by fast facies change and thin sand body reservoirs. Thus, conventional methods cannot accurately characterize the boundary of the sand body inside the prograding sand body, and the prediction accuracy is low. This study used seismic facies-controlled inversion to transform sedimentary facies characteristics on seismic profiles, and then stochastically simulated the spatial reservoir parameter based on the prior information of reservoir variables. We established a complete geostatistical variogram function and innovatively introduced adaptive regularization parameters for the noise model so that the stability and resolution of the inversion solution were improved. The application in the Kenli 10-1 oilfield shows that the inversion results are in good agreement with the staple pit, which can accurately and clearly characterize the boundary of a single prograding sand body and mudstone. This is consistent with the law of sedimentary patten of delta and achieves the purpose of accurately predicting moderately- and deep-buried oil and gas reservoirs. It is of great guiding significance for further deep oil and gas exploration and development in the future.

Quantitative Thickness Characterization of Thick Glutenite Reservoir Based on Interpretation Chart in the Bohai Oilfield
MING Jun, WANG Bo, CHEN Yao, WANG Jianli
2021, 27(5):  561-568.  DOI: 10.16108/j.issn1006-7493.2020088
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The Paleogene delta deposits in the Bohai oilfield developed glutenite reservoirs with huge thickness (greater than 100 m), and
seismic prediction of these reservoirs is difficult because of the quick lateral change and strong internal heterogeneities. To solve this problem, we propose a quantitative thickness characterization of thick glutenite reservoir based on interpretation chart in this study. Firstly, the geological model at well points was established according to the existing drilling data, and the possible reservoir change forms were analyzed by combining the existing geological data. Secondly, the geological model database was formed, and the database of corresponding forward seismic response was obtained by forward modeling. Then the seismic amplitude attributes were extracted, and the thickness interpretation chart, which represents the relation between the thickness and the seismic amplitude attributes of glutenite reservoirs, was established. Finally, the seismic amplitude attributes in the study area were extracted and projected onto the chart to characterize the quantitative thickness of thick glutenite reservoirs. This method overcomes the difficulty of conventional inversion and seismic attributes in effectively characterizing thick glutenite reservoirs. It can accurately and quantitatively characterize the thickness and internal variation of thick glutenite reservoir with interference effect.
Method of Productivity Evaluation Considering Stress Sensitivity for Reservoir with High Formation-saturation Pressure Difference in Bohai
ZHANG Zhanhua, LI zhuang, CAI Hui, CHEN Lingsong, JIA Pin
2021, 27(5):  569-576.  DOI: 10.16108/j.issn1006-7493.2020100
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The reservoir in Bohai is characterized by high formation-saturation pressure difference and large variation of reservoir pressure. In order to clarify the influence of stress sensitivity on productivity of such reservoirs, this study uses the W group reservoir in the Q oilfield as an example and obtains the change patterns of core permeability and effective stress by changing the effective stress of the core on the basis of gas-logging permeability experiment. The experiment result shows that the relationship between permeability change and the effective stress appears to be exponential. This change pattern was applied to the productivity analysis. The steady-state productivity formula considering the stress sensitivity was derived, and the productivity chart was established for comparative analysis. Considering that the stress sensitivity leads to the obvious overall decrease in productivity, there is a corresponding optimal pressure difference limit of production under different reservoir permeabilities. This is of guiding significance for the formulation of a rational production strategy for reservoirs with high formation-saturation pressure difference in Bohai.
Permeability-estimation Model of the Shahejie Formation Reservoir in the KL Oilfield, Laizhou Bay Sag
WANG Ruihong, QI Yi, LI Zhiyuan, MA Chao, WANG Yuetian, CAI Wenzhe
2021, 27(5):  577-586.  DOI: 10.16108/j.issn1006-7493.2020090
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Based on a case study of the Paleogene Shahejie Formation of the KL oilfield in the Laizhou Bay Sag, this study compares the traditional statistical model of regression with the prediction model of artificial intelligence based on BP neural network to evaluate the reservoir permeability. The target reservoir is mainly of medium to high porosity and permeability. Lithology and porosity are the main influencing factors of reservoir permeability. Based on core data analysis, the porosityparticle size binary regression model and BP neural network were established. By comparing the accuracy of the test sample set, the influence of the network structure parameters such as the number of hidden layers and the number of hidden layer nodes on the prediction results of the BP neural network model was analyzed. The effects of different logging parameters on the prediction results of BP neural network model were analyzed with the focus. The optimized BP neural network model has the highest permeability prediction accuracy for the test sample set, with an average relative error of 37%, which is 26% higher than the traditional statistical model of binary regression. For the continuous treatment of three wells in the target field, the permeability prediction results of the BP neural network model are more reasonable, which can meet the production requirements such as the production capacity analysis of the development zone.

Laboratory Experiment on Interlayer Interference of Multi-layer Commingling Production of Light Oil in the Bohai Thin Oilfield
CAI Hui, GUO Shuhao, CHENG Linsong, ZHANG Zhanhua, JIA Pin
2021, 27(5):  587-592.  DOI: 10.16108/j.issn1006-7493.2020101
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Due to low viscosity of crude oil and large permeability difference of reservoir, the interlayer interference problem during multi-layer commingling production in thin bedded light oil reservoirs is different from that of heavy oil reservoir. In order to understand the law of this problem and the production strategy can be reasonably formulated, the reservoir porosity and permeability data were made statistic analysis, and the displacement characteristics of single and commingling production under experimental conditions were studied by using two-tube parallel constant-speed displacement experiments with long cores with different permeabilities. The experimental results show that the increasing trend of water content during the displacement of oil by water in cores with different permeabilities is similar, but different from that of heavy oil. The greater the permeability difference, the more serious the interlayer interference. From the seepage mechanism, the influence law of permeability difference on interlayer interference is clarified, providing the theoretical foundation for the dividing and adjustment of reservoir.
Seismic Inversion Prediction of Dongying Formation Reservoir in#br# Liaodong Bay Basin
XIA Tongxin, LU Xinrui, LI Bin, HUANG Handong, LIU Chuanqi, YAN Hao, WANG Hongning
2021, 27(5):  593-603.  DOI: 16108/j.issn1006-7493.2020087
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Dongying Formation in the southern Liaodong Bay Basin contains a series of complex reservoirs controlled by both structure and lithology. At present, industrial oil and gas flow have been obtained after drilling. The reservoir is thin and the lithology changes greatly laterally with complex distribution and strong heterogeneity, causing great difficulties to oil and gas exploration. High-precision seismic inversion method is an effective way to solve the complexity of such oil and gas reservoirs. In this paper, the seismic phase controlled nonlinear random inversion method is used to predict the thin sandstone reservoir after stacking seismic inversion in the target interval of Dongying Formation. By reconstructing and decompressing the logging curve, the acoustic logging curve can meet the requirements of high-precision inversion. Firstly, a low-frequency velocity model is established with the constraint of seismic phase interface, and then the resolution of inversion results is improved based on the nonlinear random algorithm. Combined with the random simulation theory, the inversion results agree with to the seismic data volume. Good results have been obtained in practical application in this area, which can effectively improve the resolution of seismic data. The inversion results can characterize changes in seismic waveform and highlight the geological and sedimentary characteristics. The inversion results are in good agreement with the actual drilling data and can effectively identify thin sandstone reservoirs. Based on the inversion results, this paper characterizes the reservoir distribution of Dongying Formation in Liaodongwan depression, which provides a reliable basis for further exploration and development.

Characteristics and Main Controlling Factors of High-quality Tight Sandstone Reservoirs in the Upper Paleozoic of Dongpu Depression
WANG Xuejun, ZHU Ning, XIA Binfeng, ZHANG Yunxian, QIN Yang, YAO Suping
2021, 27(5):  604-615.  DOI: 10.16108/j.issn1006-7493.2021019
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Studying the main controlling factors of the formation of high-quality sandstone reservoirs of the Upper Paleozoic in Dongpu Depression can provide a basis for predicting high-quality reservoirs. This paper focuses on the Q3 well. Through comprehensive analyses of core observations, casting thin section, XRD, nuclear magnetic resonance cryoporometry and TIB-field emission scanning electron microscopy, the characteristics and controlling factors of the Permian reservoir in Dongpu Depression were studied. The results show that the Upper Paleozoic sandstone in Dongpu Depression is dominated by lithic feldspar and feldspar sandstones, the porosity is 0.2%-12.8% and the permeability is 0.0016-5.7 mD, which belongs to the ultra-low porosity reservoir. The residual intergranular pore, intragranular dissolution pore, carbonate mineral intergranular pore and clay mineral intergranular pore are the main pore types. Secondary pores were mainly formed by the dissolution of feldspar particles and cuttings (including tuff), which are more common in the reservoirs of P2sh Formation and P1x Formation. The high-quality reservoir is controlled by sedimentary facies, lithology, and diagenesis. The sandstone of P2sh Formation belongs to the inland river facies, the river bed is widely distributed and the sand body is developed. It is one of the most favorable reservoir system in the Upper Paleozoic of Dongpu Depression. The dissolution of feldspar is the main controlling factor of the formation of high-quality reservoir of P2sh Formation. The P1x Formation belongs to delta deposition, which was caused by volcanic activity during the sedimentary period, resulting in a large amount of tuff deposition. The kaolinite intergranular pores formed by erosion of tuff is an important mechanism for the formation of this reservoir. The main delta deposits in P1s Formation are also the main coal forming period. The acid fluid of coal system leads to the dissolution, but the large secondary increase in quartz makes the sandstone dense.

Calculation and Significance of Rock Mechanical Parameters of Deeply-buried Miocene Reservoir Rocks in the Key Offshore Exploration Blocks of the Yingqiong Basin, China
ZHANG Guanjie, WU Kongyou, FAN Caiwei, LIU Jingshou, DENG Guangjun, LIU Yujie
2021, 27(5):  616-624.  DOI: 10.16108/j.issn1006-7493.2020080
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As the key target for oil and gas exploration and development in the Yingqiong Basin, the Miocene reservoir rocks are deeply buried in offshore blocks and have rarely been cored. Consequently, insufficient research has been implemented on their mechanical parameters. In this study, full-waveform acoustic logging curves are used to calculate the rock mechanical parameters of Miocene reservoir rocks. Specifically, whole-rock mineral analysis, physical property analysis, and mercury intrusion
experiments are conducted to identify the key factors that influence the rock mechanical parameters. The Miocene reservoir rocks
feature a Young’s modulus range of 20-50 GPa, a Poisson’s ratio range of 0.1-0.35, an internal friction angle range of 20°-35°,
and a tensile strength range of 5-30 MPa. Laterally, heterogeneity of mechanical parameters is seen in the same layer. Vertically, these mechanical parameters present a weak positive correlation with the burial depth. Four factors are demonstrated to be crucial for rock mechanical parameters, namely rock porosity, clay mineral content, brittle mineral content, and pore radius. The results of this study provide reliable basic data for the simulation of insitu stress field, evaluation of reservoir fractures, and optimization of the target fracturing scheme. Moreover, the results of this study provide a theoretical basis for evaluation of geological and rock mechanical parameters of deeply buried reservoirs.